Which is an example of a tumor-specific antigen?

• A. Cea
• B. BCR/ABL fusion protein
• C. CA 125
• D. PSA

Answer: (B)

Tumor-specific antigens are abnormal proteins produced only by cancer cells due to genetic changes, creating targets that don’t exist in normal tissues. The BCR/ABL fusion protein is the classic example: it arises from a cancer-specific chromosomal translocation (Philadelphia chromosome) and produces a novel protein not found in healthy cells. That uniqueness makes it a true tumor-specific antigen.

In contrast, markers like CEA, CA125, and PSA can be elevated or present in some cancers but are also found in normal tissues or benign conditions, so they’re considered tumor-associated or tissue-specific markers rather than tumor-specific antigens.